Direct Detection of Sound Wave by Light Development of Optical Wave Microphone with No Diaphragm

Optical wave microphone is a novel method to measure audio and ultrasonic sounds by a laser beam with no diaphragm. In this method, ultra-weak diffraction light generated by sound is optically Fourier transformed and converted into an electrical signal. In this study, in order to improve the S/N ratio for practical use, the external resonator structure of He-Ne laser is used as a sound sensor and the sound signal amplification property is theoretically and experimentally examined. We succeeded in sound signal amplification by this method.